This can happen if Free Monitor for Google wasn't closed correctly - it saves project data upon closing. So if some error has occured in that time, the project might become corrupted and doesn't open on the next run.

So if next time such thing happens follow this step-by-step:
1. Suppose you ran Free Monitor for Google and found your data is gone - do NOT close the program now! - as this will overwrite your project with empty data.
2. Instead immediately open the Project menu and select Restore project.
3. Your automatic backups are stored in AppData folder. It is:
Under Windows XP/2000 - C:\Documents and Settings\username\Application Data\Free Monitor for Google\
Under Windows Vista/7 - C:\Users\username\AppData\Roaming\Free Monitor for Google\
4. Open the appropriate folder in the Restore dialog and look for project.gmp.backup file. It may not be visible, so switch to show all files in the dialog if necessary.
5. Now Free Monitor for Google will restore the data from your last backup - the one saved in your previous run of Free Monitor for Google. That's why it was important to NOT close the program in the pt.1
6. Close Free Monitor for Google correctly so it can save restored data to the project.